Changes in GTK+ 3.22

The CSS parser has gotten a bit more selective in what it accepts as
valid values for the font: shorthand. Following the CSS specification,
at least a size and a family name are required now. If you want to
change an individual facet of the font, like the weight, use the
individual CSS properties: font-weight, font-size, font-family, etc.

The CSS parser now warns about some more constructs that are not according
to the CSS spec, such as gradients with a single color stop. Instead,
you can just use image(<color>).

The “ignore-hidden” property has not been working properly
for a long time, and we've not documented it as broken and deprecated.
The recommended alternative for reserving space of widgets that are not
currently shown in the UI is to use a GtkStack (with some 'filler'
widget, e.g. an empty GtkBox, in another page).

GtkHeaderBar now respects the hexpand property for its custom title
widget and its packed children. This change may inadvertently cause the
layout of those children to change, if they unintentionally had hexpand
set before.

The behavior of the expand flag in GtkTablesGtkAttachOptions has been
changed to (again) match the behavior in GtkBox and in GTK+ 2.x. These
options don't cause the table itself to expand.